The present invention is a vibratory device of the imbalance type for generating vibrations with an amplitude which is selectively variable while the shaft is rotating.
A typical application of such device is for soil and asphalt compaction machines. In the compaction of soil, asphalt, and similar materials by means of vibratory rollers, it is often necessary to adapt the amplitude of the vibration to the nature of the bedding in order to achieve the desired compaction effect. As a general rule, the greater the amplitude of vibration, the higher the compaction effect. However, when vibrations of relatively large amplitude are used, as the compaction process approaches its final stages, it often happens that the machine, acting on the substantially compacted surface, begins to run irregularly, producing high stresses in all of its parts. By reducing the vibration amplitude in the final compaction stages, the irregular motion of the machine can be stopped. By selecting a desired initial vibration amplitude, and by adjusting the vibration amplitude during the compaction process, it is possible to obtain the maximum compaction effect for the type of compaction machine in use, suited for the particular type of bedding. At the same time, over-compaction can be avoided or at least reduced.
A pre-requisite for this operation is the use of a vibration element with a continuously adjustable amplitude. Previously, known vibratory devices of this general type effect amplitude adjustment by using one or more mass elements arranged on a rotating shaft, and capable of being pivoted in relation to the shaft and to one another. Adjusting devices interact with the mass elements for the purpose of achieving a continuously variable vibration amplitude while the shaft is rotating.
Another known method for generating vibrations with a continuously variable amplitude is to use a liquid contained in a container, applied to the rotating shaft. The liquid volume is increased and decreased during rotation of the shaft, forming an imbalance element and thereby varying the amplitude of vibration movement generated during rotation.
These systems, however, are often complicated and require complex adjustment mechanisms. In certain hydraulic systems the volume of oil under pressure is also in rotation, while necessitates a rotary seal with the danger of leakage and troublesome heat generation in the oil as a result.